"Cold limits the geographical distribution, yield and growth season of both native vegetation and crops. Temperate perennials show an increase in freezing tolerance under low temperatures. This cold acclimation process involves massive changes in gene expression and metabolite contents. Plants lose freezing tolerance after transfer back to warm temperatures by de-acclimation. While cold acclimation has been studied extensively, de-acclimation and the persistence of the acclimated state under warm conditions (memory phase) have not attracted much attention. Therefore, the physiological and molecular mechanisms that determine the extent of this memory under a given condition remain to be identified. Also, how such a memory phase may influence a subsequent low temperature response has only rarely been investigated on the phenotypic level (i.e. as increased freezing tolerance termed ‘re-acclimation’) and not at all on the molecular level. In this project we aim to: (1) physiologically and biochemically characterize the cold acclimation, memory and re-acclimation responses in natural accessions of Arabidopsis thaliana and its close relative Thellungiella salsuginea. (2) Investigate the metabolic reprogramming as a result of the treatments using GC-ToF-MS metabolite profiling and (3) unravel the transcriptional and post-transcriptional responses of the plants to these treatments using microarray hybridization on total mRNA as well as qRT-PCR on total mRNA and mRNA derived from polysomes. Objective 4 is to identify preferentially regulated functional classes of genes and identify metabolic pathways of particular importance during the different temperature responses in the two species using various bioinformatic approaches. The results will increase our understanding of regulation and mechanisms of de-acclimation and the potential of plants to ‘remember’ stressful conditions and modify their reactions to a subsequent low-temperature event."